The present invention relates to a heat exchanger including high-temperature fluid passages and low-temperature fluid passages defined alternately by alternately disposing a plurality of first heat-transfer plates and a plurality of second heat-transfer plates.
Such heat exchangers have already been proposed in Japanese Patent Application Nos.7-193208 and 8-275057 filed by the applicant of the present invention.
The above conventional heat exchangers suffer from the following problem: The partitioning between a high-temperature fluid passage inlet and a low-temperature fluid passage outlet and the partitioning between a low-temperature fluid passage inlet and a high-temperature fluid passage outlet are achieved by bonding a partition plate by brazing to a cut surface formed on the heat-transfer plate by cutting its angle-shaped apex portion. For this reason, the bonded portions of the cut surface of the heat-transfer plate and the partition plate are in line contact with each other. To reliably perform the brazing, the precise finishing of the cut surface is required, and moreover, even if the finishing is performed, it is still difficult to provide a sufficient bonding strength.
The above conventional heat exchangers also suffer from the following other problem: axially opposite ends of the heat-transfer plate are cut into angle shapes to define the fluid passage inlet and outlet. Therefore, a drifting flow of fluid is generated from the outer side toward the inner side as viewed in a turning direction due to a difference between the lengths of flow paths on the inner and outer sides as viewed in the turning direction in a region where a fluid flowing into the heat exchanger obliquely with respect to an axis in the vicinity of the fluid passage inlet is turned in the direction along the axis, and in a region where the fluid flowing in the direction along the axis is turned in an inclined direction with respect to the axis in the vicinity of the fluid passage outlet. For this reason, the flow rate on the outer side as viewed in the turning direction is decreased, while the flow rate on the inner side as viewed in the turning direction is increased, whereby the heat exchange efficiency is reduced due to the non-uniformity of the flow rate.
The above conventional heat exchanger is formed into an annular shape by folding a folding plate blank in a zigzag fashion to fabricate modules each having a center angle of 90xc2x0 and combining four of the modules in a circumferential direction. However, if the heat exchanger is formed by combination of a plurality of modules, the following problems arise: the number of parts is increased, and moreover, four bonded points among the modules are produced, and the possibility of leakage of the fluid from the bonded portions is correspondingly increased.
The present invention has been accomplished with the above circumstances in view, and it is a first object of the present invention to ensure that a sufficient bonding strength is provided without a precise finishing of the ends of the heat-transfer plate. It is a second object of the present invention to suppress of a drifting flow of a fluid generated at fluid-direction changing portions in the vicinity of the fluid passage inlet and outlet of the heat exchanger thereby to prevent a reduction in heat exchange efficiency. It is a third object of the present invention to decrease the number of parts of the heat exchanger and to maintain the leakage of the fluid from the bonded portions of the folding plate blank to the minimum.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a heat exchanger, comprising a plurality of first heat-transfer plates and a plurality of second heat-transfer plates disposed radiately in an annular space defined between a radially outer peripheral wall and a radially inner peripheral wall, and a high-temperature fluid passage and a low-temperature fluid passage which are defined circumferentially alternately between adjacent ones of the first and second heat-transfer plates by bonding pluralities of projections formed on the first and second heat-transfer plates to one another, axially opposite ends of each of the first and second heat-transfer plates being cut into angle shapes each having two end edges, thereby defining a high-temperature fluid passage inlet by closing one of the two end edges and opening the other end edge at axially one end of the high-temperature fluid passage, defining a high-temperature fluid passage outlet by closing one of the two end edges and opening the other end edge at the axially other end of the high-temperature fluid passage, defining a low-temperature fluid passage outlet by opening one of the two end edges and closing the other end edge at axially one end of the low-temperature fluid passage, and defining a low-temperature fluid passage inlet by opening one of the two end edges and closing the other end edge at the axially other end of the low-temperature fluid passage, characterized in that flange portions formed by folding one of apex portions of the angle shape are superposed one on another and bonded together, whereby the high-temperature fluid passage inlet and the low-temperature fluid passage outlet are partitioned from each other by the superposed flange portions, and further flange portions formed by folding the other apex portion of the angle shape are superposed one on another and bonded together, whereby the high-temperature fluid passage outlet and the low-temperature fluid passage inlet are partitioned from each other by the superposed further flange portions.
With the above arrangement, in the annular heat exchanger in which the fluid passage inlets and outlets are defined by cutting the axially opposite ends of the heat-transfer plates into angle shapes, the flange portions formed by folding the apex portions of the angle shape are superposed one on another and bonded together, whereby the fluid passage inlet and outlet are partitioned from each other by bonding a partition plate to the superposed flange portions. Therefore, as compared with the case where a partition plate is bonded in a line contact state to the cut surfaces formed by cutting the heat-transfer plates, the superposed flange portions can be bonded together in a surface contact state, thereby not only increasing the bonding strength, but also eliminating the need for a precise finishing of the cut surfaces. Therefore, the bonding of the projections on the heat-transfer plates and the bonding of the flange portions can be accomplished in a continuous flow, leading to a reduction in processing cost.
If a folding plate blank including the first and second heat-transfer plates which are alternately connected together through first and second folding lines is folded in a zigzag fashion along the first and second folding lines, and portions corresponding to the first folding lines are bonded to the radially outer peripheral wall, while portions corresponding to the second folding lines are bonded to the radially inner peripheral wall, the number of parts can be reduced, and moreover, the misalignment of the first and second heat-transfer plates can be prevented to enhance the processing precision, as compared with the case where the first and second heat-transfer plates are formed from different materials and bonded to each other.
If the flange portions are folded into an arcuate shape and superposed one on another, and the height of projection stripes formed along angle-shaped end edges of the first and second heat-transfer plates is gradually decreased in the flange portions in order to close the fluid passage inlets and outlets, it is possible to prevent a gap from being produced between the projection stripes, while preventing the mutual interference of the projection stripes abutting against one another at the flange portions to enhance the sealability to the fluid.
To achieve the first object, according to a second aspect and feature of the present invention, there is provided a heat exchanger, comprising a plurality of first heat-transfer plates and a plurality of second heat-transfer plates which are formed into a rectangular shape, and a high-temperature fluid passage and a low-temperature fluid passage which are defined alternately between adjacent ones of the first and second heat-transfer plates by bonding a pair of long sides of each of the first and second heat-transfer plates to a first bottom wall and a second bottom wall, bonding a pair of short sides of each of the first and second heat-transfer plates to a first end wall and a second end wall, and further bonding a plurality of projections formed on the first and second heat-transfer plates to one another, a high-temperature fluid passage inlet and a high-temperature fluid passage outlet which are defined in the first bottom wall so as to extend along the first and second end walls, respectively and which are connected to the high-temperature fluid passage, and a low-temperature fluid passage inlet and a low-temperature fluid passage outlet which are defined in the second bottom wall so as to extend along the first and second end walls, respectively and which are connected to the low-temperature fluid passage, characterized in that flange portions formed by folding the pair of short side portions are superposed one on another and bonded together, and the first and second end walls are bonded to the superposed flange portions, respectively.
With the above arrangement, in the rectangular parallelepiped heat exchanger in which the pair of long sides of the pluralities of the heat-transfer plates formed into the rectangular shape are bonded to the bottom walls, respectively, while the pair of short sides are bonded to the end walls, respectively, and the fluid passage inlets and outlets are defined at longitudinally opposite ends of the bottom walls, the flange portions formed by folding the short sides of the heat-transfer plates are superposed one on another and bonded together, and the fluid passage inlet and outlet are partitioned from each other by bonding the superposed flange portions to the end wall. Therefore, as compared with the case where the end walls are bonded in a line contact state to end surfaces formed by cutting the heat-transfer plates, the superposed flange portions can be bonded in a surface contact state to one another, thereby not only increasing the bonding strength, but also eliminating the need for a precise finishing of the cut surfaces. Therefore, the bonding of the projections on the heat-transfer plates and the bonding of the flange portions can be accomplished in a continuous flow, leading to a reduction in processing cost.
If a folding plate blank including the first and second heat-transfer plates which are alternately connected together through the first and second folding lines is folded in a zigzag fashion along the first and second folding lines, and portions corresponding to first folding lines are bonded to the first bottom wall, while portions corresponding to the second folding lines are bonded to the second bottom wall, the number of parts can be reduced, and moreover, the misalignment of the first and second heat-transfer plates can be prevented to enhance the processing precision, as compared with the case where the first and second heat-transfer plates are formed from different materials and bonded to each other.
To achieve the second object, according to a third aspect and feature of the present invention, there is provided a heat exchanger, comprising a plurality of first heat-transfer plates and a plurality of second heat-transfer plates which are disposed radiately in an annular space defined between a radially outer peripheral wall and a radially inner peripheral wall, whereby a high-temperature fluid passage and a low-temperature fluid passage are defined alternately in a circumferential direction between adjacent ones of the first and second heat-transfer plates, axially opposite ends of the first and second heat-transfer plates being cut into an angle shape each having two end edges, respectively, thereby defining a high-temperature fluid passage inlet by closing one of the two end edges and opening the other end edge at axially one end of the high-temperature fluid passage, defining a high-temperature fluid passage outlet by closing one of the two end edges and opening the other end edge at the axially other end of the high-temperature fluid passage, defining a low-temperature fluid passage outlet by opening one of the two end edges and closing the other end edge at axially one end of the low-temperature fluid passage, and defining a low-temperature fluid passage inlet by opening one of the two end edges and closing the other end edge at the axially other end of the low-temperature fluid passage, and tip ends of large numbers of projections formed on opposite surfaces of the first and second heat-transfer plates being bonded together, characterized in that a pitch of arrangement of the projections is different between the axially opposite ends and an axially intermediate portion of each of the first and second heat-transfer plates.
With the above arrangement, in the annular heat exchanger in which the fluid passage inlets and outlets are defined by cutting the axially opposite ends of the heat-transfer plates into the angle shape, the pitch of arrangement of the projections formed on the heat-transfer plate is different between the axially opposite ends and the axially intermediate portion of the heat-transfer plate. Therefore, it is possible to prevent a drifting flow from being produced at a fluid-direction changing portion to provide an enhancement in heat exchange efficiency and a reduction in pressure loss, by changing the fluid flow resistance in the vicinity of the fluid passage inlets and outlets by the projections.
In areas facing the inlets and outlets of the high-temperature fluid passage and the low-temperature fluid passage, if the pitch of arrangement of the projections in a direction substantially perpendicular to the direction of flowing of fluid passed through the inlets and outlets is dense in an area portion nearer to a base end portion of the angle shape and sparse in an area portion nearer to the tip end portion, the flow resistance on a radially inner side of the direction-changing portion where the fluid is easy to flow because of the short flow path can be increased by the dense arrangement of the projections, and the flow resistance on a radially outer side of the direction-changing portion where the fluid is difficult to flow because of the long flow path can be decreased by the sparse arrangement of the projections, thereby preventing a drifting flow from being produced in the fluid-direction changing portion to provide an enhancement in heat exchange efficiency and a reduction in pressure loss.
If the pitch of arrangement of the projections of the first and second heat-transfer plates is set such that the unit number of heat transfer is substantially constant in a radial direction at an axially intermediate portion of each of the first and second heat-transfer plates, it is possible to radially uniformize the profile of temperature of the heat-transfer plate to avoid the reduction in heat exchange efficiency and the generation of undesirable thermal stress. When the heat transfer coefficient of each of the first and second heat-transfer plates is represented by K; the area of each of the first and second heat-transfer plates is represented by A; the specific heat of the fluid is represented by C; and the mass flow rate of the fluid flowing in the heat transfer area is represented by dm/dt, the unit amount Ntu of heat transfer is defined by the following equation:
Ntu=(Kxc3x97A)/[Cxc3x97(dm/dt)]
If the projections are arranged at the axially intermediate portion of each of the first and second heat-transfer plates, so that they are not lined up in the direction of flowing of the fluid passed through the axially intermediate portion, the fluid is agitated sufficiently by the projections, leading to an enhanced heat exchange efficiency.
To achieve the second object, according to a fourth aspect and feature of the present invention, there is provided a heat exchanger, comprising a plurality of first heat-transfer plates and a plurality of second heat-transfer plates which are formed into a rectangular shape, and disposed in parallel, so that a pair of long sides thereof are bonded to a first bottom wall and a second bottom wall and a pair of short sides thereof are bonded to a first end wall and a second end wall, thereby defining high-temperature fluid passage and low-temperature fluid passage alternately between adjacent ones of the first and second heat-transfer plates, a high-temperature fluid passage inlet and a high-temperature fluid passage outlet which are defined in the first bottom wall so as to extend along the first and second end walls, respectively and which are connected to the high-temperature fluid passage, and a low-temperature fluid passage inlet and a low-temperature fluid passage outlet which are defined in the second bottom wall so as to extend along the second and first end walls, respectively and which are connected to the low-temperature fluid passage, and large numbers of projections formed on opposite surfaces of the first and second heat-transfer plates and bonded together at tip ends of the projections, characterized in that the pitch of arrangement of the projections is different between longitudinally opposite ends and a longitudinally intermediate portion of each of the first and second heat-transfer plates.
With the above arrangement, in the rectangular parallelepiped heat exchanger in which the fluid passage inlets and outlets are defined at the longitudinally opposite sides of the rectangular heat-transfer plates, the pitch of arrangement of the projections formed on each of the heat-transfer plates is different between the longitudinally opposite ends and the longitudinally intermediate portion of the heat-transfer plate. Therefore, when the fluid is turned in the vicinity of the fluid passage inlet and outlet, the fluid flow resistance can be controlled by the projections to prevent the generation of a drifting flow directed inwards in the turning direction to provide an enhancement in heat exchange efficiency and a reduction in pressure loss.
In areas facing the high-temperature and low-temperature fluid passage inlets and outlets, if the pitch of arrangement of the projections in the direction substantially perpendicular to the direction of flowing of the fluid passed through the inlets and outlets is dense in an area portion farther from the first and second end walls and is sparse in an area portion nearer to the first and second end walls, the flow resistance on a radially inner side of the direction-changing portion where the fluid is easy to flow because of the short flow path can be increased by the dense arrangement of the projections, and the flow resistance on a radially outer side of the direction-changing portion where the fluid is difficult to flow because of the long flow path can be decreased by the sparse arrangement of the projections, thereby preventing a drifting flow from being produced in the fluid-direction changing portion to provide an enhancement in heat exchange efficiency and a reduction in pressure loss.
To achieve the third object, according to a fifth aspect and feature of the present invention, there is provided a heat exchanger, comprising a plurality of first heat-transfer plates and a plurality of second heat-transfer plates which are disposed radiately in an annular space defined between a radially outer peripheral wall and a radially inner peripheral wall, whereby a high-temperature fluid passage and a low-temperature fluid passage are defined alternately in a circumferential direction between adjacent ones of the first and second heat-transfer plates, a folding plate blank including the plurality of first heat-transfer plates and the plurality of second heat-transfer plates which are alternately connected together through first and second folding lines, the folding plate blank being folded in a zigzag fashion along the first and second folding lines, and portions corresponding to the first and second folding lines being bonded to the radially outer peripheral wall and the radially inner peripheral wall, respectively, thereby disposing the first and second heat-transfer plates radiately, defining the high-temperature fluid passage and the low-temperature fluid passage alternately in the circumferential direction between the adjacent first and second heat-transfer plates, defining a high-temperature fluid passage inlet and a high-temperature fluid passage outlet so as to open into axially opposite ends of the high-temperature fluid passage, and defining a low-temperature fluid passage inlet and a low-temperature fluid passage outlet so as to open into axially opposite ends of the low-temperature fluid passage, characterized in that the single folding plate blank is folded in the zigzag fashion over 360xc2x0, and opposite ends thereof are superposed one on another and bonded together in an area including the first and second folding lines.
With the above arrangement, in forming the annular heat exchanger by folding the folding plate blank including the first and second heat-transfer plates which are alternately connected together through the first and second folding lines in the zigzag fashion, the single folding plate blank is folded in the zigzag fashion over 360xc2x0, and the opposite ends thereof are superposed one on another and bonded together in an area including the first or second folding line. Therefore, the heat exchanger can be formed by a minimum number of parts or components, and moreover, the number of bonded zones of the folding plate blank is the minimum, one, thereby suppressing the possibility of leakage of the fluid to the minimum. In addition, the opposite ends of the folding plate blank is merely cut and hence, it is unnecessary to conduct a special processing, leading to a reduced number of processing steps. Moreover, the folded portions of the folding plate blank including the first or second folding line are superposed one on another and hence, the bonding strength is increased. Further, the circumferential pitch of the adjacent first and second heat-transfer plates can be regulated finely only by changing the cutting positions of the folding plate blank to regulate the number of the first and second heat-transfer plates.